The present invention relates to an electron beam apparatus, for example, a scanning electron microscope which is suitable for performing observation or length measurement of a contact hole or a line pattern by irradiating an electron beam on a specimen, such as a semiconductor device, in order to evaluate a semiconductor production process.
The scanning electron microscope has hitherto been used for observation or length measurement of a contact hole or a line pattern of the submicron order (less than 1 .mu.m) in a semiconductor device specimen.
With recent advancement in semiconductor integrated circuit technology, there has been a tendency for a circuit element to be formed in three-dimensional directions, so that, for example, contact holes and deep holes and grooves (hereinafter represented by contact holes) for separation of condensers and elements are formed in the specimen surface.
Incidentally, when an electron beam is irradiated on the interior of a contact hole for the purpose of observing the bottom of the contact hole, most of the secondary electrons discharged from the bottom of the contact hole impinge on the side wall of the contact hole, are captured thereby, and are thus prevented from escaping from the contact hole. Accordingly, the contact hole is considered to be equivalent to a Faraday cup.
As an approach to a method of detecting secondary electrons in a contact hole with high efficiency, a technique is proposed in, for example, JP-A-62-97246 according to which an electrode for drawing out secondary electrons from the contact hole is provided between an objective lens and the specimen surface to generate a positive electric field near the specimen surface so that and secondary electrons will be drawn out by the positive electric field.
Also, JP-A-63-274049 proposes a technique according to which a cylindrical electrode disposed in a pole piece of an objective lens is supplied with a positive voltage to generate a positive electric field near the specimen surface in order that secondary electrons generated in the specimen surface are drawn out efficiently and guided to the side, facing an electron source, of an objective lens. The present inventors have attempted to observe a contact hole by using an apparatus having the construction described in the above literature, but have failed to obtain an excellent image. In other words, the inside of the contact hole could not be observed.